1. Field of the Invention
The present invention relates to tempered water mixing systems where cold and hot water supplies are thermostatically blended to provide a tempered discharge outflow of water at a selected temperature.
2. Description of the Prior Art
Thermostatic mixing valves (TMVs) have been in use for many years to control the temperature of water supplied to a delivery point. Thermostatic control valves of this general type are well known, e.g., as shown in U.S. Pat. Nos. 4,739,793; 4,767,052; and 5,647,531. These valves are well known to those skilled in the art. TMVs are capable of delivering water at a preset temperature, as well as preventing water flow in the event of the failure of the cold water supply. They are used extensively in hospitals, nursing homes and similar facilities. A particular application would be, for example, for supplying water to plumbing fixtures such as showers, large medical bathing systems or as a master mixing valve supplying numerous plumbing fixtures simultaneously. These valve systems are often installed in bath and shower areas, to regulate the flow of bathing water and to ensure precise water temperature in varying supply water conditions. A typical example is a valve that maintains shower water temperature when another water appliance is being operated. A sudden drain on the cold water supply may drop the cold water pressure, while leaving the hot water pressure relatively constant, thus increasing outlet water temperature due to an imbalance between hot and cold inlet water flow. The TMV is used to accommodate such variances while maintaining a preset outlet temperature.
Mechanical TMV's operate using a temperature sensitive element such as, for example, a bimetallic element or a spring element. In use, hot and cold water is supplied to the valve via respective hot and cold inlets. The water mixes inside the valve and is then delivered to a desired location through an outlet. In use the temperature sensitive element is linked to the hot and cold inlets so as to control the flow of hot and cold water into and thru the valve.
If the resulting mixed water temperature is too hot, the temperature sensitive valve element will typically expand or move in response to the temperature increase. This causes the flow of water through the hot water inlet to be reduced and/or the flow of water through the cold water inlet to be increased. This in turn causes a corresponding reduction in the mixed water temperature.
Similarly, if the mixed water temperature falls to low, the temperature sensitive element will contract, or move in the opposite direction, causing the hot water inlet to be opened further and/or the cold water inlet to be closed further, thereby causing the mixed water temperature to increase. In this manner, the TMV can be used to provide water at a predetermined temperature.
One disadvantage of this typical class of mechanical TMV is that valves of this type tend to be quite expensive, for example, on the order of $8000-$10,000 per valve. Another disadvantage of the prior art temperature balancing valves and many electronically controlled mixing valves described in the prior art is the inability to stabilize outlet water temperature at extremes of flow rate. This is due to several technical issues such as the velocity of water in the plumbing lines, the thermal lag of the water temperature sensor and mechanical overshoot in the thermal governor cartridge assembly or motor/belt drive of electronically controlled thermostatic valves.
A need exists, therefore, for an electromechanical temperature regulation system for providing tempered mix water which is simple in design and yet reliable in operation and which can be produced more economically than presently available TMV systems.
A need exists for such a system for providing tempered water at a preset temperature without significant temperature fluctuation.
A need exists for such a system having a desired response time for the establishment of a steady flow of tempered water having the desired preset temperature from the time a user opens a flow control valve.